Given the following compounds and their vapor pressures (vp). arrange them in increasing (lowest to highest) order of boiling points. ethane (c2h6); vp= 841 mm hgpentane (c5h12); vp=420 mm hgisopropyl alcohol (c3h5oh); vp=31.5 mm hgacetone (c3h6o); vp=185 mm hgisopropyl alcohol < acetone < pentane < ethaneethane < pentane < isopropyl alcohol < acetoneethane < pentane < acetone < isopropyl alcoholacetone < isopropyl alcohol < pentane < ethanethe strength of the intermolecular forces is also needed to determine the order.

Increasing order of boiling point

isopropyl alcohol > acetone > pentane > ethane

Explanation:

Vapor pressure - the pressure exerted the gaseous molecules , on the walls of the container is called the vapor pressure.

Boiling point - the temperature at which the the vapor pressure of the liquid equals the external atmospheric pressure.

Both boiling point and vapor pressure are linked by the inter molecular forces between the atoms.

The compound with stronger inter molecular forces are tightly held , hence more amount of energy is required to vaporize. Therefore, higher boiling point , and in turn the vapor pressure will be lower .

And the compound with weaker inter molecular forces are loosely held , hence less amount of energy is required to vaporize. Therefore, lower boiling point , and in turn the vapor pressure will be higher .

Therefore,

The vapor pressure and boiling point will have an inverse relation.

Given , The vapor pressure of the compound in increasing order -

isopropyl alcohol < acetone < pentane < ethane .

Hence, the order of boiling point will be exactly reverse.

So , the Increasing order of boiling point,

isopropyl alcohol > acetone > pentane > ethane

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